U.S. Pat. No. 4,742,940 discloses a dispenser for flowable materials, such as toothpaste, which includes a hollow barrel open at its lower end and closed at its upper end. A plunger in the form of a hollow tube is telescopically arranged in the barrel to create a material chamber therebetween. In the preferred operation of that device, material is dispensed from a dispensing spout by resting the plunger on a support surface and moving the barrel downwardly so as to cause relative motion of the upper end of the barrel toward the upper end of the piston thereby forcing material out of the dispenser through the dispensing spout. In such a dispenser it is essential that there be a proper seal between the piston and tube. A proper seal is one that will effectively assure that the material will be dispensed only through the dispensing spout. The seal, however, must also permit relative sliding contact between the piston and barrel. In the '940 patent, peripheral contact surfaces in the form of solid ring-like structures are provided on the outer surface of the piston for making sealing engagement with the inner surface of the barrel. The '940 patent also discloses that a sealing material, such as a washer may be provided to the contact surface to further aid in the piston action and assure a sealing contact.